Rotary valves have long been known and used in various forms for internal combustion engines and compressors. The usage of such valves soon fell into disfavor however, in spite of some desirable features inherent to their design. Sealing of rotary valves has heretofore required a precise, close tolerance fit-up, somewhat at odds with the realities of the application. Over and above the costs exacted by the required manufacturing precision, a greater problem has been high maintenance requirements. Differential heating and expansion of parts, further aggravated by the build-up of deposits, has caused valve sticking and poor reliability. As a result, the less demanding poppet valve has come to enjoy virtually universal acceptance.
In recent years, fuel economy and pollution control requirements have changed the standards of the marketplace, giving the desirable features of rotary valves a new significance. Rotary valves have a potential for unobstructed flow, providing cylinder filling and exhaust efficiencies exceeding those of the most sophisticated multi-valve poppet arrangements.
Moreover, the symmetrical, straight through rotary valve design as taught by Smith U.S. Pat. No. 3,896,781 or Negre et al. U.S. Pat. No. 4,506,636 as well as others, need only rotate at one-quarter engine speed in a four-cycle engine application. Between openings, the cylindrical surface of the valve rotor becomes a portion of the combustion chamber. Since alternating, relatively cool surface areas and passageway ends are engaged on each intake or exhaust stroke, the fuel/air mixture flow is not threatened by premature, "hot spot" ignition and higher compression ratios are tolerable. Moreover, since poppet exhaust valve cooling is normally aided by impingement of the incoming charge during an overlap of inlet and exhaust open periods, some of the charge flows through and around the exhaust valve. This adversely affects both emission controls and fuel economy. Rotary valves have heretofore not realized true commercial success, mainly because of cost, reliability and maintenance considerations, but the attractive potential of rotary valve engines is clear. Inasmuch as the market has now accepted the expensive overhead cam, four valve-per-cylinder engine designs at the high end, relative cost is no longer a decisive factor.
An object of the present invention is therefore, to provide a rotary valve assembly which can operate reliably with generous clearances so that differential thermal expansion and combustion deposits will not be a source of maintenance problems.
A second object of the present invention is to provide this reliable rotary valve system without any compromise of flow area.
Yet another object of the present invention is to provide a rotary valve system which can be readily adapted to pre-existing conventional engines as an economical, easily assembled after-market replacement cylinder head assembly or an original equipment option.
The potential flow area of rotary valves is related to the diameter of the valve body and the angular duration of the valve open period. Although no precise relationship is mandated, valve body diameter should be two-thirds of the engine piston diameter or greater in order to allow effective flow area. The valve rotor of the present invention is fitted into its housing for free rotation with sufficient clearance to avoid binding due to heat distortion or combustion deposits. The valve rotor rotates once for every four crankshaft revolutions in a four-cycle engine so that the combustion chamber is alternately opened to opposite ends of a diametral port and closed by the opposed cylindrical surfaces. Sealing elements make the only contact between the valve rotor and the housing and, in order to seal the combustion chamber volume during the compression and power strokes, these elements surround the closing area thus, two sets of elements are involved. The two sets of seals alternate in sealing the combustion chamber volume, which reduces the severity of their service requirement and, rotating at one-quarter engine speed, the contact velocity of the sealing elements is relatively low.